This invention relates to digitally programmable analog-signal manipulating circuits and more particularly to programmable integrator circuits having an analog transfer function comprised of variables and parameters wherein the value of each one of a pair of the parameters is capable of being set and or altered to a desired value by introducing a digital signal at a corresponding group of programming terminals.
A simple example of a digitally programmable analog-signal manipulating circuit is a standard digital to analog converter (DAC) employed in an unconventional manner to provide a programmable voltage divider (PVD). Standard DAC circuits are described by L. P. Huelsman, J. G. Graeme and G. E. Tobey at pages 336-339 in their book Operational Amplifiers, McGraw Hill, 1971. Such a PVD is further described herein below.
Another example of a digitally programmable analog-signal manipulating circuit is described D. J. Allstot, R. O. Brodersen and P. R. Gray in their paper entitled An Electrically-Programmable Switched Capacitor Filter, published in the IEEE Journal of Solid-State Circuits, Vol. Sc-14, No. 6, December 1979, pages 1034-1041. There, the analog-signal manipulating circuit is a second-order filter employing active integrators connected in tandem. The integrating (feedback) capacitor in each integrator consists of a digitally programmable capacitor array so that the filter transfer function has programmable poles. It is also known to use a fixed resistors voltage divider preceding the integrator resistor.
It is an object of this invention to provide a digitally programmable analog-signal manipulating circuit having a transfer function containing the product of two separately programmable parameters, one parameter being rendered programmable by electrically altering the value of a capacitor and the other by electrically altering the ratio of a voltage divider.